1. Field of the Invention
The present invention relates to an apparatus for disposing of fuel-vapor, especially to an apparatus for disposing of fuel-vapor which can control the air-fuel ratio of an exhaust gas within the proper range regardless of the altitude at which an automobile having the apparatus operates.
2. Description of the Related Arts
Fuel-vapor evaporating from a fuel tank is absorbed in a charcoal canister, and is properly purged in an inlet pipe as fuel in order to improve fuel consumption and to avoid air pollution.
Because atmospheric pressure decreases when the automobile runs at a high altitude, the evaporation of fuel stored in a fuel tank increases. As the amount of the fuel-vapor absorbed in a charcoal canister increases, it is necessary to prolong the purge period. However, because a throttle valve must be made more open at a high altitude than at a low altitude, the purge period and the total purge amount decreases.
To solve the above-mentioned problem, a purge control apparatus which increases the opening of the purge valve in order to compensate for a decrease in atmospheric pressure by using an altitude compensating valve has been proposed (see Unexamined Patent Publication (Kokai) No. 58-27865).
It is, therefore, necessary to purge as often as possible so far as the fuel-vapor purged from the charcoal canister does not disturb the air-fuel ratio control, because the large amount of fuel-vapor exerts a harmful influence upon the air-fuel ratio control. The above-mentioned purge control apparatus does not take account of this effect.
Therefore, a deterioration in drivability or of exhaust gas emissions due to the disturbance of the air-fuel ratio control produced by the purge control cannot be avoided.